Television and like system



28, 9- M. BOWMAN-MANIFOLD El AL 218L572 TELEVISION AND LIKE SYSTEM Filed April 17, 1936 2 Sheets-Sheet l IN VENTORS M/CHIIEL BOWMIN-AIIINIFOLD W/LL/lt/ SPENCER P-"RC/V/IL 7K4 2 Sheets-Sheet 2 lNVENTORS M/CHAEL BOWMAN-MANIFOLD W/LL/AM SPENCER PERC/l AL ATTORNEY M. BOWMAN-MANIFOLD El" AL TELEVISION AND LIKE SYSTEM Filed April 17, 1956 NOV. 28, 1939.

0 T a i w x I A: X" o 1205? n 8 5 9 m as v: m 9 NR 0 6 A w mm s I TO 4 I w T E W f. mm W m B m m we P W m w m ,T W M w H X y: F. 3 T 7 m I W 7 .m .JJI... H 7 s W s 7 n w I 7 W m w x mm M w R n E "Wm PM .0 0 M W 2; w F E the line signals; in one known arrangement of Patented Nov. 2s, 1.939 I 2,181,572

UNITED STATES PATENT OFFICE TELEVISION AND LIKE SYSTEM Michael Bowman-Manifold, Worpleodon Station, and William Spencer Percival, Hanwell, England, assignorc to Electric & Musical 1ndustries Limited, Hayes, Middlesex, England, a British company Application April 17, 1936, Serial No. 14,944

In Great Britain April 9, 1935 9 Claims. (0]. I'm-$9.5)

The present invention relates to television and The present invention has for its principal oblike systems, and is particularly concerned with ject to provide improved or simplified means for systems in which an object of which an image is to attaining synchronism in television systems in be transmitted is completely scanned in a pluwhich interlaced scanning is achieved by the use rality of traversals thereof, the lines scanned in of the third of the three methods outlined above, one traversal being intercalated with those that is, the method in which the field-traversal scanned in another; for convenience, this method signals are all arranged to be in substantially the of scanning will be referred to as interlaced scansame phase with respect to the line signals. ning, and each of the traversals of the object will The present invention accordingly provides a be called a field traversal. television or like transmission system comprising Various methods of achieving interlaced scanmeans for scanning an object of which an image ning are known in which the area traced out by is to be transmitted to generate trains of picture the scanning spot is displaced in the direction of signals having intervals between trains, the lines frame scanningfor example, in the vertical scanned in one field traversal of said object being directi0nafter each field traversal the amount intercalated between the lines scanned in the next of displacement is made equal to an integral subfield traversal, means for generating line synmultiple of the vertical distance moved by the chronising signals for transmission in said interscanning spot in scanning a line. The frame vals and field-traversal synchronising signals for shift thus introduced is reduced to zero after transmission at the end of each traversal of said sufficient field traversals have been made to scan object, said field-traversal signals being all arthe object completely, and the frame-shift freranged to ur in su st ntial y t sa p se quency is accordingly an integral sub-multiple of relationship with respect to said line signals, the field-traversal frequency. means for transmitting said picture signals and Three fundamentally different methods of synline and field-traversal synchronisin i and chronising the frame-shift motion at the receiver a receiver arranged to e erate under the inwith that taking place at the transmitter which fluence of said field-traversal sig a s, fie d-t avare already known are as follows: In the first, the ersal scannin Oscillation O which Successive synchronising signals which are transmitted for cy es v dl t durations. the difielence controlling the field-traversal motion are caused between said durations being equal to the time to recur at constant frequency, but successive c p by the scannin of a act on of a line. signals are arranged to be in suitably different According t a f atu of the invention. a phases with respect to the synchronising signals ceiver suitable for use in a system as set forth in which are transmitted for controlling the linethe P d g D p comprises a generator scanning motion; the latter signals are caused to r en r i fiel r v r cannin scillarecur at constant frequency. In the nd tions under the control of applied" field-traversal method, line synchronising signals are generated synchronising signals w c e all in the same at constant frequency, and successive field-travphase With respect to the Said line synchronising ersal signals are arranged to occur in different signals, wherein frame-shift means are P ded phases with respect to the line signals, the method for Varying in a cyclic manner the P e o s d differing from the first method in that the fieldfield-traversal scanning oscillation with respect to traversal signals do not recur at constant frethe app e field-traversal synchronising als. quency. The third method is characterised i The synchronising signals referred to in the two that the field-traversal signals are all arranged to preceding P p s may be constituted y he in substantially the same phase with respect to p es having amplitudes lying Outside the range of picture signal amplitudes, and transmitted along the same channel as the picture signals; in this case, the synchronising signals can be freed from the picture signals at the receiver by an amplitude selection. The field traversal pulses may be constituted by certain of the line pulses which are made of longer duration than the remainder, as described in British Patent Specification No. 425,220. 7

The present invention further provides a method of television or like transmission in which,

this kind, the field-traversal signals are arranged to recur at a constant frequency, although this is not an essential feature, and interlacing is achieved at a receiver by causing the field-traversal signals to control the generation of both a field-traversal scanning oscillation and an auxiliary frame shift oscillation, the two oscillations being superimposed upon one another and applied to control the field-traversal operation of the picture-reconstituting device.

at the transmitter, an object of which an image is trains of picture signals having intervals between trains, which method comprises transmitting a line synchronising signal in each of said intervals, said line signals being of substantially constant frequency and wave form, transmitting a field traversal synchronizing signal in each of the intervals between successive field traversals, the initial portions of said field-traversal signals being arranged to be substantially in phase with the initial portions of said line synchronising signals and each field-traversal signal being of a wave form different from that of the field-traversal signal preceding and succeeding it and from that of the line synchronising signals, and, at the receiver,

utilising said field-traversal signals to generate a field-traversal scanning oscillation of such a nature that, in the reconstituted image, lines traced out in successive field traversals are intercalated with one another.

The invention further provides a method of television or like transmission in which,:at the transmitter, an object of which an image is to be transmitted is scanned by a process of interlaced scanning to generate, in' each field traversal, trains of picture signals having intervals between trains, which method comprises transmitting a line synchronising signal in each of said intervals, said line signals being of substantially constant frequency. and wave form, transmitting a field traversal synchronising signal in eachof the intervals between successive field traversals, the initial portions of said field-traversal signals being arranged to be substantially in phase, with the initial portions of said line synchronising signals and each field-traversal signal being of a wave form different from that of the field-traversal signal preceding and succeeding it and from that of the line synchronising signals, and at the receiver, utilising, said field traversal signals to generate a field-traversal scanning oscillation. and utilising certain of said field-traversal signals to control the operation of frame-shift means, said means serving to cause successive cycles of said scanning oscillation to difier in duration by a time substantially equal to that occupied by the scanning of l/nth of a'line, where n is the number of field traversals in which said object is completely scanned.

In the methods according to the two preceding paragraphs, the field-traversal signals may be arranged to have a duration greater than that of said line synchronising signals, and less than the time period of the line signals, and the line and field-traversal signals may all be arranged to have the initial portions of their wave forms steep and of substantially the same shape, whereby said field-traversal signals may be utilised, at the receiver, to control the operation of line scanning during intervals between field traversals.

'The invention also provides a television or like transmission system of the kind in which, at the transmitter, an object of which an image is to be transmitted is scanned by a process of interlaced scanning to generate, in each field traversal, trains of picture signals having intervals between trains, said system comprising a transmitter including means for transmitting a line synchronising signal in each of said intervals, said line signals being of substantially constant frequency and wave form, and means for transmitting a field traversal synchronising signal in each of the intervals between successive field traversals, the

initial portions of said field-traversal signals being arranged to be substantially in phase with the initial portions of said line synchronising signals, and each field-traversal signal being of a wave form different from that of the field-traversal signal preceding and succeeding it and from that of the line synchronising signals, and a receiver including a generator of field-traversal scanning oscillations and means for' applying to said generator received field-traversal signals, or signals derived therefrom, to control the initiation of successive cycles of said scanning oscillatio said generator being arranged so that, by virtue o e diiference in the wave forms of successive field traversal signals, there can be generated a fieldtraversal scanning oscillation of such a nature that, in the reconstituted image, lines traced out in successive field traversals are intercalated with one another.

Other features of the invention will appear from the following description and appended claims.

Reference is now directed to the accompanying diagrammatic drawings, in which various embodiments of the inventionare represented by way of example. In the drawings,

Fig. 1 shows schematically a part of a television receiver accordingto the invention,

Fig, 2 illustrates a modified arrangement according to the invention,

Figs. 3 and represent a form of synchronising signal which may be employed in carrying this invention into efi'ect,

Fig. 5 is a schematic representation of a television system according to the invention, and

Figs. 6 and 7 illustrate details of the system of Fig. 5.

In the description of the arrangements of Figs. 1 and 2, it will be assumed that. the receiver is to be employed for the reception of picture signals and synchronising signals arriving along the same channel, the synchronising signals being injected into the transmission channel, which will be assumed to be constituted by a carrier wave, in the blacker-than-black sense with respect to the picture signals. The synchronising signals will further be assumed to be of the kind described in British Patent Specification No. 425,220, including field traversal or frame signals each of which comprises a single broad pulse occurring in an interval between successive trains of picture signals. It is to be understood, however, that the invention is not limited to the use of synchronising signals of the kind referred to. It will be further assumed throughout the description of the drawings that it is desired to achieve interlaced scanning in two field traversals at the receiver.

Referring to Fig. 1, received picture and syn chronising signals are applied for example, from the demodulating detector of a wireless receiver, between the control grid of a screen grid valve 2 and earth, it being arranged that the synchronising signals are in the negative sense and are at such an amplitude that they reduce the anode current of the valve 2 to zero at their peaks. The anode of valve 2 is connected to the positive terminal of a source (not shown) of anode current, the negative terminal of which is earthed, through a resistance 3, and a condenser 4 is connected between the anode of valve 2 and earth. The screen grid and cathode of valve 2 are biased by means of a potential divider comprising resistances 5 and 6, decoupling condensers 'l and 8 being provided as shown.

The anode of valve 2 is also connected tothe function of which will be made clear hereinafter.

The winding l3 of transformer II is connected between a tapping on resistance 5 and the screening grid of a valve l4, while the winding l5 has one end connected to'earth and, its other end connected through a condenser I! to the control grid of valve l4. A lead is also taken from the junction point of winding l5 and condenser to the input of amplifier IS. A leak resistance I8 is connected between the control grid of valve l4 and earth, while the anode thereof is connected through a resistance l9 to the positive terminal of the source of anode current.

'lhe valve l4 and its associated circuit elements act in well-known manner as a blocking oscillator, a saw-tooth potential wave at the fieldtraversal frequency being set up across a condenser connected between the anode of'the valve l4 and earth. The function of the circuit 'associated with valves 2 and 9 is to separate arriving field-traversal pulses from line pulses, and to ensure that only the former are effective upon blocking oscillator H. The operation of the apparatus so far described will be more fully explained hereinafter; it is pointed out here, however, that the method of separation mployed forms the subject of co-pending. United States application Serial No. 59,022.

As is well known, the blocking oscillator valve becomes alternately insulating and conducting, the change from one condition to the other being initiated by an applied synchronizing pulse which causes an oscillation to be set up between the control and screen grid circuits. The eifect of this oscillation isto cause grid current to flow, and the condenser becomes charged to such a negative potential that the oscillation is blocked, anode current ceases to flow, and the cycle is completed. The charge on condenser leaks away through resistance l8, and just before the flow of anode current recommences, a new synchronising pulse arrives, and the cycle recommences.

' The potential difference across the winding '|5 of transformer thus comprises effectively a series of pulses at the field-traversal frequency, and these pulses are amplified in amplifier |5and applied, through a delay network comprising series inductance 2| and shunt condenser 22, between the screen grid and cathode of a second blocking oscillator valve 23 which is adapted to set up an oscillation of saw-tooth wave form and of one half the field-traversal frequency across condenser 24. Of these pulses applied to blocking oscillator 23, every alternate one is eifective in initiating a change from the insulating to the conducting state. A condenser 25 and a resistance 26 are connected in series between the junction point .of elements 2| and 22 andthe screen grid of valve 23. The variable resistance 21, associated with grid condenser 28 and transformer 29, permits adjustment to be made of the frequency of the saw-tooth oscillation generated, and the anode of valve 23 is connected to the positive terminal of the anode current source through a variable resistance 30 by means of which the amplitude of the saw-tooth oscillation may be adjusted.

The saw-tooth oscillation set up across condenser 24 is applied through condenser 3| to the control grid of a so-called cathode-follower valve I2, the anode of which is connected to the positive terminal of the anode current source through a resistance 33, and to earth through a decoupling condenser 34. The cathode of valve I2 is earthed through two resistances and 36 in series, and a grid leak 32 is connected between the grid and the join of resistances. 35 and 36.

The magnitude of resistances 35 and 35 in series is made large compared with vthe reciprocal of the mutual conductance of valve H, the potential of the cathode of which accordingly follows substantially accuratelychanges in the potential of the control grid.

The operation of the arrangement of Fig. l is as follows: I a

Each synchronising pulse arriving at the control grid of valve 2 causes that valve to become insulating, and at each pulse, condenser 4 charges up to a positive potential dependent upon the duration of the pulse. There is thus set up across condenser 4 a series of triangular voltage pulses of which those due to the field-traversal synchronising pulses are of greater amplitude than those due to the line pulses.

The positive potential at the cathode of valve l2, and hence of the cathode of diode 9, is arranged to be greater at all times than the peak voltage set up at the anode of diode 9 on the occurrence of a line synchronising pulse, but it is arranged that on the occurrence of 'a field traversal pulse, current flows in diode 9, and hence in transformer winding i0, and blocking oscillator I4 is triggered off.

Now the voltage at the cathode of diode 9 is not constant, since a potential difference of sawtooth wave-form, and of one half the fieldtraversal frequency, is set up across the two resistances 35 and 35 in series. ,Thus at the arrival of one field-traversal pulse, the saw-tooth oscillation set up across resistances 35 and 36 may have reached approximately one half of its maximum amplitude, while at the arrival of the next field-traversal pulse, the oscillation will have reached approximately its maximum value and the potential at the anode of diode 9 must reach a greater positive value before current flows in the diode and blocking oscillator I4 is triggered off. By adjustment of the amplitude of the saw-tooth oscillation generated by blocking oscillator 23, it can be arranged that if the first of the two field-traversal pulses causes the blocking oscillator H to be triggered off at the end of a line, the next field-traversal pulse will cause the blocking oscillator I4 to be triggered oif approximately midway between the end of one line and the beginning of the next. The function of delay circuit 2|, 22 is to ensure that oscillator 23 is triggered off slightly later than oscillator H, at the ends of alternate field traversals, so as to prevent the occurrence of a reaction effect from oscillator 23 to oscillator vl4.

It must, of course, be arranged that the set of alternate field-traversal pulses which is eifectively retarded in the manner described is the correct set, so that scanning at the receiver takes place in the same manner as at the transmitter: in other words, if lines I, 3, 5 etc. are scanned in one field traversal at the transmitter, and lines 2, 4, 5 etc. in the next, then oscillator 23 must be so adjusted that it looks in synchronism with that set of alternate pulses from generator |4 that, at the receiver, the sequence of line scanning is 1, 2, 3 etc. and not 2, 1,. 4, 3, 6, 5 etc.

By the use of the apparatus described, fieldexample, field-traversal pulses which all occur in intervals between successive trains of picture signals) are caused to produce interlaced scanning at a receiver in a plurality of scans each of which comprises an integral number of lines plus a fraction of a line. It is to be noted thalt by causing the blocking oscillator 23, which may be regarded as the oscillator which controls frame shift, to oscillate at an integral fraction of the field-traversal frequency which is smaller than one half, for example, one third, interlaced scanning in more than two, for example in three, field traversals can be achieved. It is also to be noted that it is not essential that the received field-traversal pulses shall be of constant frequency, although in practice this will usually be so.

A modified arrangement according to the invention, which is suitablefor use at a receiver in which it is desired to achieve interlacing in two traversals, will now be described with reference to Fig. 2; in the description of this figure, it will be assumed that the received signals have the same form as that discussed with reference to Fig. 1.

Referring to Fig. 2, received .picture and synchronising signals are applied, for example from the demodulating detector of a wireless receiver, not shown, to a separator 40 which serves flrstly to free the synchronising signals from picture signals and secondly to separate the field-traversal pulses from the line pulses, for example, by frequency selection, or in a manner such as that described with reference to Figf l. g

The field-traversal pulses are fed in the negative sense to the control grid of a double anode screen grid valve 41 through a grid condenser 48 and leak 49. The circuitof anode 60 of valve 41 includes a resistance 58, and potential differences set up at the anode 60 of valve 41 are applied through a condenser 6| and a resistance 62 arranged to provide a relatively weak coupling to the anode of a triode valve 52, the cathode of which is earthed.

The second anode, 63, of valve 41 is connected to the positive terminal of the anode current source through resistance 64, and to the screen grid of a valve 4| through a condenser 65 and a resistance 68 in series. Valve 4|, in association with transformer 42, condenser 43, and resistances 44 and -45, functions as a blocking oscillator to set up In operation, valve 52 functions as a blocking oscillator to set up a potential of saw-tooth waveform and one half the field-traversal frequency across condenser 54. Due to the efiect of the separator 40 1 in separating the field-traversal pulses from the line pulses, the field-traversal pulses arriving at blocking oscillator 4| are arranged to be approximately triangular in their general form, and the efiect of the auxiliary, or frame-shift saw-tooth oscillation fed to oscillator 4| through condenser 43 from oscillator 52 is that two successive field-traversal pulses arriving at oscillator 4| cause that oscillator to be triggered off after different time intervals from the beginning of the corresponding pulse. By a suitable choice of the value of condenser 54, .for example,:the time diflerence referred to may be made equal to the time, of scanning of one half of a line, in which circumstances the saw-tooth oscillation .set up across condenser 46 may be employed to provide interlaced scanning in two traversals. As in the arrangement of Fig. 1, it is. of course, essential that the .correct .set of alternate field-traversal pulses should be retarded.

constituted by three pulses c which are broader than the pulses b of Fig. 3. The pulses a, b and c all have leading edges which recur, throughout the whole synchronising signal, at the line scanning frequency, and the pulses b and can thus serve at the receiver to control the synchronisation of the line scanning operation during the field-traversal intervals. Various ways in which synchronising signals of the kind shown in Figs. 3 and 4 may be utilised according to the present invention will now be described by way of example with reference to the television system shown diagrammatically in Fig. 5.

Referring to Fig. 5, picture signals for transmission are generated by means of an image transmitting tube such as that known by the trade name Iconoscope having a mosaic screen electrode 1| associated with a signal output resistance 12; signals setup across the latter are fed to a transmitter 13.

The line pulse generator 14 generates pulses of the kind shown at a in Figs. 3 and 4, and fieldtraversal pulse generators 15 and 18 generate pulses of the kind shown at b and 0 respectively, generators 14, 15 and 16 all operating to generate pulses recurring at the line frequency. During the scanning of lines at the transmitter, it is arranged that line pulses from generator 14 are fed to transmitter 13, while at the ends of successive field traversals, pulses from generator 15 or generator 18 respectively are fed to transmitter 13; the selection of pulses from generators 14, 15 and 16 is performed by the automatic switches 11, which may be of any known or suitable type, such as thermionic valve switches. The composite synchronising signal fed to transmitter 13 is of the form shown in Figs. 3 and 4, and is mixed with the picture signals in the blacker-than-black sense. The apparatus for controlling scanning at the transmitter may be controlled by synchronising pulses from generators 14, 15 and 16, and the scanning apparatus at the transmitter may have substantially the same form as that employed at the receiver, which will now be described.

The receiver 18 is fed with signals received from transmitter 13 by a suitable aerial system 19, and supplies picture signals to a picturereconstituting cathode ray tube 80. The output of the demodulating detector of the receiver 18 is fed to separator 8| which frees the synchronising pulses from picture signals, and feeds the whole series of pulses to a generator 82 of line scanning oscillations, the latter being applied to the horizontal deflecting coils 83 of the tube 38; the synchronising pulses from separator 8| diodes 88 and 88 respectively as shown- The blocking oscillators associated with wind-'- ings'. IM and 188 are arranged to oscillate reaisins scanning oscillation' -of; such a-nature that, in-

operation of afield-traversal scanning oscillation generator: 88 which feedsthevertical defiecting coils-88of the tube 88;- w v .".lhe generatorll is..arranged togenerate a the reconstituted image; lines traced out in suc-' cessive field traversals are intercalated with one another. One-manner in which this may beachieved will :now be described with reference v to Fig. 6. Y

8 Referring to Fig. 6, whichillustrates one form which the selector 88 of Fig." 5 may take, the

received synchronisingsignals, free from picture signals. areapplied from separator 8I to the Figs. land 2, to delay the operation of the blockcontrol grids of two tetrode valves 81 and 88 through a condenser 88 associated with leak resistance 88; The cathodesof valves 81 and 88 are connected together, and to earth through resistance 8| shunted by by-pass condenser 82. The anode. ofvalve 81 is connected through a resistance 88 to the positive terminal of a source (not shown) of anode current, the negative terminal of' which is earthed. and the anode oi valve 88 is connected to the positive terminal of the source through a resistance 88. A resistance 88 is connected between the positive terminal of the source and the cathode of valves 81 and 88, and a tapping point on resistance 85 is connected to the screening grids of the valves; the tapping point is earthed' through by-pass condenser 88.

A potential divider resistance 81 is connected between the positive terminal of the-anode current source and earth, and the cathodes of two diodes 88 and 88 are connected to adjustable tapping points in resistance 81. The anode of diode 88 is connected, through a coil I88 constituted by one winding of a blocking oscillator transformennot sliowmto the anode of valve 88, and the anode of diode 88 is connected through the winding I8I' of a second blocking oscillator transformer (not shown) to-the anode of valve 81; A condenser I82 is connected between the anode of valve 88 and-earth; and a condenser I88 is connected between the anode of valve; 81 and earth;ydecoupling condensers I88 and I85: areiconnectedbetween the cathodes of spectively at the field-traversal frequenqmand one half the field-traversal frequency respec-.

tively, and. the output of the blocking'oscillator associated with winding I88 may be employed. in the manner already describedwith reference to ingoscillator associated with windingl8i at alternate field traversals.

Alternatively, the outputs .of the two blocking.

oscillators may be added together in the same sense to furnisha scanning oscillation which may.

beemployed to provide interlacedscanning. I

. Inoperation the received synchronising signals are applied toivalves 81 and 88 in the negative sense, and at sucha level that the fiow of anode currentifin these valves is interrupted during each synchronising}. pulse. Accordingly during each pulse, a. charging current. flows to condensers I82 and I88-,these condensers being rapidly discharged I during intervals between synchronisingpulses. There is. accordingly set up across each of. condensers I82 and I88 a series of voltage pulses in the the pulses due to the signals b andv c (Flgs;' 3

and!v .beingxof greaterzamplitude than those -.due

to signals a.'-1:. 'l'.he scatliodeof- :diode- 88 is 1 connected to a pointsuch? a wpositive: potential in resistance 81 that fno current flows: therein when a line pulse ai'is'roperative onvalve "81,

but-that current fiows' .lwhe'n" either: a I pulse 1) orapulse c is operative: cathode of diode '88, however, is connected-toia'point'at a more positive wpotentialt; s01. that only" the -broaderpulses c cause current tdfiow therein. 'Ihe'blocking oscillators associated-with windings I88 andI8I .are thus controlled in the manner described.

A further arrangement according to the' invention is illustrated" in Fig. 7, whichshows a form which theselectorfl and field-traversal generator 88 of FiguSmay take.-- Referring to Fig. '1, synchronising pulses from separator. 8i are fed through condenser I88 to-the'.control grid of tetrode valve I81 in the positive sense; condenser I88 isassociated with leak resistance I88, and it is arranged that the control grid of valve I81 biases itself in such a mannersby fiow of grid current, that no current flows in the valve except in thepresence eta-synchronising The anode of valve I81 is connected through a resistance I88 to the positiveterininal of a source (not shown) of anode current, the negative'terminal of which is earthed. and the cathode of valve I81 is earthed through a resistance 'I I8 shunted by condenser III. A lead II8 is taken from the anode of valve I81 to the line scanning oscillation generator", Fig.5.

The resistance' II8and condenser III serve to so" chosen that the potential set up across resist v ance 8 reaches the criticalvalue after a; time, subsequen to the arrival'of the leadingiedgeoi the first of the pulses c, which'is' less than-thetime after. the arrival of the fir'stof the pulses b at which thecritical value is attained. This'time difference is'made equal'to that-occupied by the scanning of ,one halif of a :line, so thatthe scanning oscillation setup across condenser 281s of a nature such that it-can'be employed to produce interlaced scanning in two-ifieldtraversals.

The arrangements describedwith reference to Figs. 3 to 7 have employed a synchronising signal in which successive field-traversal signals difler-' or comprise pulses which difier--in-duration;"it will, however, be: clear to those versed in the art that, if desired, field-.traversal'signals diflering m amplitude, or in. a both duration and amplitude, may be employed. Insuch .a case, the received field traversal signals may convenientlybe'iconverted at therece'iver, in any'knownor suitable manner, into derived: signals-having" diil'erent durations, in which case apparatus of: the hnd described with referenceto Figs. :6iand '1-may beemployed. It is further. to be :understood that the invention isynot limited to systems=in-which interlacing is achieved in two field traversals only.

6 areas."

The application of the invention other than to the art;.

We 01811112 i 1. A picture transmission system comprisingmeansfor scanning an obiectof which an'im'age is to be transmitted to generate trainsof picture signals having intervals between trains, the lines scanned in one field traversal of said object being intercalated between the lines scanned in the next field traversal, means for generating line synchro nizing signals for transmission in said intervals and field traversal synchronizingsignalsfor transmission at the end of each traversal of said object, each said field traversal synchronizing signal beginning substantially simultaneously with the beginning of certain line synchronizing signals, means for transmitting said picture signals and line and field traversal synchronizing signals, and a receiver apparatus including means to generate under the influence of said field traversal signals a field traversal scanning oscillation of which successive cycles have different durations, the difference between said durations being equal to the time occupied by the scanning of a line.

2. In a television system, means for interlacedly scanning in a line-for-line manner an image area to produce a sequence of trains of signal energy, means to develop line synchronizing signals representing the completion of each scanned line of the image, means to develop field traversal synchronizing signals at the completion of each field traversal, said field traversal synchronizing signals beginning substantially simultaneously with said line synchronizing signals,

means to transmit all of said signals, means to nals received. 4

3. In a television system, means for interlacedly scanning in a llne-for-line manner an image area to produce a sequence of trains of signal energy, means to develop line synchronizing signals representing the completion of each scanned line of the image, means to develop field traversal synchronizing signals at the completion of each field traversal, said field traversal-synchronizing signals beginning substantially simultaneously with said line synchronizing signals, means to transmit all of said signals, means to receive said transmitted signals, a generator at the receiver for generating field traversal scanning oscillations under the control of the applied field traversal synchronizing signal, and in phase with chronizing signals at the completion of each field traversal, said field traversal synchronizing signalsbeginning substantially simultaneously with said line synchronizing signals, means to transmit all of said signals, means to receive said transmitted signals, a blocking oscillator for developing field traversal scanning oscillations under-'the control of the received field traversal synchronizing signals, frame shifting means including means for developing an auxiliary oscillation at a sub-harmonic of the field traversal synchronizing frequency for controlling the oscillator whereby the phase relationship of the field traversal scanning oscillations may be cyclically varied.

5. In a television system, means for interlacedly scanning in. a line-for-line manner an image area to produce a sequence of trains of signal energy, means to develop line synchronizing impulses of. unidirectional form following each scanned line of the image, means to. develop at the completion of each field traversal a field traversal signal comprising at least one impulse of a duration longer than the line impulse, the field traversal signal frequency being a sub-multiple of the line signal frequency, means for transmitting all of said signals so that the beginning of each said field traversal impulse is substantially coincidental with the beginning ofsaid line synchronizing impulse, means for receiving all of said signals, a blocking oscillator at the receiver for generating field traversal scanning oscillations, means for controlling the developed oscillations in accordance with the received synchronizing impulses, and means for varying in cyclical manner the phase of the developed field traversalrimpulse oscillations at a frequencywhich is an integral sub-multiple of the field traversal frequency;

6. In a television system, means for interlacedly scanning in a line-for-line manner an image area to produce a sequence of trains of signal energy, means to develop line synchronizing signals representing the completion of each scanned line of the image, means to develop field traversal synchronizing signals at the completion of each field traversal, said field traversal synchronizing signals beginning substantially simultaneously with said line'synchronizing signals, means to transmit all of said signals, means to receive said transmitted signals, a blocking oscillator at the receiver for generating field traversal scanning oscillations in accordance with the received field traversal sigrials,'and an auxiliary blocking oscillator associated with thefirst blocking oscillator and adapted to generate a saw-tooth oscillation of a frequency which is an integral sub-multiple of the field traversal frequency for varying in cyclic manner the phase of the field traversal scanning oscillations with respect to the field traversal synchronizing signals received.

7. The method of television transmission which comprises interlacedly scanning an image area to generate wave trains of picture signal energy having time intervals separating successive trains, transmitting, line synchronizing signals each of substantially constant frequency and waveform in each of said intervals, initiating field traversal synchronizing signals substantially simultaneously with the beginning of certain of said line synchronizing signals, transmitting said field traversal synchronizing signals in .each of the intervals between successive field traversals, each field traversal signal being of a wave form different in-length from that preceding and succeeding it and also from the line synchronizing signal, generating at a receiving point a field traversal scanning oscillation, and controlling the generated scanning oscillation at the receiver in accordance with the length of the transmitted field traversal signals so that the lines traced in successive field traversals are interlaced one with the other.

8. The method of television transmission which comprises interlacedly scanning an image area to generate wave trains 0! picture signal energy having time intervals separating successive trains, transmitting line synchronizing signals each of substantially constant frequency and wave form in each of said intervals, initiating field traversal synchronizing signals substantially simultaneously with the beginning of certain of said line synchronizing signals, transmitting said field traversal synchronizing signals in each of the intervals between successive field traversals, each field traversal signal being of a wave form different from that preceding and succeeding it and also from the line synchronizing signal, gen- 'erating at a receiving point a field traversal 9. In a television system, means for scanning an image in a line-for-line manner according to an interlaced scanning pattern to develop a series of image signals for each scanning field, means for transmitting following each line of scanning a line synchronizing signal, said signals being of constant frequency and wave form, means for transmitting a field traversal synchronizing signal in each of the intervals between successive field traversals, said field traversal signals beginning substantially simultaneously, with said line synchronizing signals and each field traversal signal being of a wave form different from that of the field traversal signal preceding and succeeding it and from that of the line synchronizing signal, means for receiving all 01 the signals, said receiving means compristion so that successive field traversals are interlaced one with the other.

MICHAEL BOWMAN-MANIFOLD. 

